The company also forecast 2013 adjusted earnings of $7.15 to $7.25 a share on about 10% revenue growth. Analysts surveyed by Thomson Reuters expect $7.27 a share on a 9% rise in revenue to $5.98 billion.

Biogen on Thursday said a new version of its blockbuster multiple-sclerosis drug Avonex was successful in a late-stage trial, strengthening the company's stable of drugs for the degenerative nerve disease. However, the overall market for such injectable drugs is expected to decline sharply amid a growing market for oral-pill-based drugs. Biogen's own BG-12 pill could be approved and launched in the U.S. as soon as March.

Biogen has been beefing up its sales force and readying its manufacturing supply chain as some drugs in its late-stage product pipeline have been drawing closer to entering the market.

Research and development costs rose 1.8% in the latest period while selling, general and administrative costs jumped 32%.

Biogen reported a profit of $292.1 million, or $1.23 a share, down from $300.2 million, or $1.22 a share, a year earlier. Excluding items such as stock-option expense, amortization and restructuring charges, per-share earnings fell to $1.40 from $1.51. Revenue increased 6.9% to $1.42 billion.

Analysts polled by Thomson Reuters most recently projected earnings of $1.46 a share on revenue of $1.39 billion.

In the latest quarter, sales of Avonex rose 7.1% to $753.2 million.

Shares closed Friday at $146.20 and were inactive premarket. The stock is up 23% over the past year.

Write to Tess Stynes at tess.stynes@dowjones.com and Melodie Warner at melodie.warner@dowjones.com